No major change in the direction of ongoing studies on leukocytes and platelets have been projected. The soft agar tissue culture technique for the analysis of hematopoietic colonies on the EM leve will be used withtwo goals in mind: 1) The identification of "factors" which indue differentiation of precursor cells into definitive cell types and 2) the analysis of pathologic specimens under similar conditions. Thymus factor (TF) prepared in the laboratory of Dr. J.F. Bach in Paris will be used in these cultures to attempt differentiation of lymphocytes. Mitogen stimulated lymphocytes will be used in feeder layers in th hope of promoting the differentiation of eosinophils. Studieson lymphocytes from patients with Sezary Syndrome and/or mycosis fungoides will concern primarily the possible elucidation of the biochemical composition and function of the cytoplasmic microfibrils we have found in these cells. Work on platelets of patients with thrombocytopenia and myelofibrosis initiated during the past year will continue as planned. BIBLIOGRAPHIC REFERENCES: Zucker-Franklin, D.: Relationship of cellular structure and function in normal and neoplastic lymphoid cells. Arch.Int.Med., 135: 55,1975. Schriber, R.A. and Zucker-Franklin, D.: Induction of blood eosinophilia by pulmonary embolization of antigen-coated particles. The relationship to cell medited immunity. J.Immunol.,114: 1348, 1975.